The present invention is directed to a method and apparatus for correcting a spinal deformity, such as scoliosis, kyphosis, and/or lordosis.
A wide variety of instrumentation and methods for use thereof are known for the correction of spinal deformities, such as scoliosis, kyphosis, and lordosis. Many of the known instruments utilize bone screws, also referred as bone anchors, that are implanted into vertebrae. Once implanted, the bone screws are used to mount suitable spinal fixation instrumentation, such as clamps, rods, and plates. Such spinal instrumentation is then used to achieve and maintain correction of the spinal deformity and stabilize the corrected vertebrae while the vertebrae fuse together.
Most known bone screws use a conventional screw design, i.e. a solid shank, with one or more external thread convolutions. The solid shank and external threads of the conventional bone screws can cause the bone screws to displace an undesirably large amount of bone when implanted. Such conventional bone screws typically require a large amount of torque to implant the screw into a vertebral body. Furthermore, the resistance of the conventional screw to being pulled axially from the bone is dependent upon the surface area of the bone that interfaces with the screw threads.
It is also known to use a corkscrew-style helical spike as a tissue anchor. The known corkscrew-style tissue anchors, when implanted, displace less bone than the conventional bone screws, but are generally not able to withstand high tensile loads without structural failure. European Patent No. 0 374 088 A1 discloses a bone screw having a twin-corkscrew design. In this twin-corkscrew design, which is formed by drilling a passage up through a screw having a solid shank and then machining out the material between the two corkscrews, the junction of the corkscrews with the shank is unlikely to be capable of structurally withstanding high tensile loads and repetitive fatigue loads. This structural weakness in the design of the screw in the EP 0 374 088 document is further compounded by the corkscrews having a larger overall diameter than the head of the screw where torque is applied.
One of the more challenging applications of a bone screw is implantation of the screw into the cancellous bone of a vertebral body. Unfortunately, many of the known bone screws, such as those described above, can be susceptible to toggling in the vertebral body and can also pull out of the vertebral body due to the substantial forces on the screws from human body movement and muscle memory. In order to achieve a high pull-out resistance, it is common to use additional screws, which results in an undesirably large amount of bone being displaced. Alternatively, in order to achieve a high pull-out resistance, it is also known to thread a bone screw all of the way through a vertebrae and place a nut on the opposite side. However, use of such a nut increases the complexity of the surgical procedure.
As mentioned above, implanted bone screws are typically used to mount spinal fixation instrumentation, which is then used to achieve and maintain correction of a spinal deformity, such as scoliosis. Various methods and associated fixation instrumentation are known for achieving correction of a spinal deformity, but most are limited by the relatively low pull-out resistance of the known bone screws. New methods and new spinal instrumentation for achieving correction of a spinal deformity would be possible if screws with a higher pull-out resistance were available.
Hence, it is desirable to provide an apparatus for implantation into vertebrae in a minimally invasive endoscopic procedure with a reduced amount of insertion torque required. The desirable apparatus would, when implanted, be highly resistant to toggling in the vertebrae and to being pulled out of the vertebrae despite the substantial forces on the apparatus from human body movement and muscle memory. Further, the desirable apparatus could enable, and even include, new spinal instrumentation and methods for correcting spinal deformity.
The present invention provides an apparatus for correcting spinal deformity. The apparatus comprises at least one anchor for implantation into a vertebral body. The at least one anchor, when implanted, is resistant to toggling in the vertebral body and to being pulled from the vertebral body. The at least one anchor includes a platform having a first surface for facing the vertebral body. The platform includes at least one passage extending transversely through the platform. The at least one passage is for receiving a cable connected with another vertebral body. The at least one anchor further includes at least one helical spike for embedding into the vertebral body upon rotation of the platform. The at least one helical spike projects from the first surface on the platform and extends around a longitudinal axis. The at least one helical spike has a tip portion at a distal end which penetrates into the vertebral body as the platform is rotated.
In accordance with another feature of the present invention, an apparatus for correcting spinal deformity is provided. The apparatus comprises first and second anchors for implantation into first and second vertebral bodies, respectively. The anchors, when implanted, are resistant to toggling in the vertebral bodies and to being pulled from the vertebral bodies. Each of the first and second anchors includes a platform having at least one passage extending transversely through the platform. Each of the first and second anchors further includes screw means for embedding into one of the vertebral bodies upon rotation of the platform. The screw means projects from the platform on each of the first and second anchors and has a tip portion at a distal end which penetrates into a respective one of the vertebral bodies as the platform is rotated. At least one cable extends through the at least one passage in the platform on each of the first and second anchors. The at least one cable is tensionable to cause relative movement between the first and second vertebral bodies.
In accordance with yet another feature of the present invention, an apparatus for correcting spinal deformity is provided. The apparatus comprises at least two anchors for implantation into separate vertebral bodies, respectively. The at least two anchors, when implanted, are resistant to toggling in the vertebral bodies and to being pulled from the vertebral bodies. Each of the at least two anchors includes a platform having at least one passage extending transversely through the platform. Each of the at least two anchors further includes at least two helical spikes for embedding into one of the vertebral bodies upon rotation of the platform. The at least two helical spikes project from the platform on each of the at least two anchors and have tip portions at a distal end which penetrate into a respective one of the vertebral bodies as the platform is rotated. At least one cable extends through the at least one passage in the platform on each of the at least two anchors. The at least one cable is tensionable to cause relative movement between the vertebral bodies. A spinal fixation implant extends between and is connectable with the platform on each of the at least two anchors.
In accordance with still another feature of the present invention, a method for correcting spinal deformity is provided. According to the inventive method, at least two anchors are provided for implantation into separate vertebral bodies. Each of the at least two anchors includes a platform having at least one passage extending transversely through the platform. Each of the at least two anchors further includes screw means for embedding into one of the vertebral bodies upon rotation of the platform. The at least two anchors are embedded in the separate vertebral bodies. The at least two anchors are connected with at least one cable that extends through the at least one passage in the platform on each of the at least two anchors. The at least one cable is then tensioned to cause relative movement between the vertebral bodies.